<html>
    <head>
        <style>
            #jihui{
                text-align: center;
                color: crimson;
                
            }
            .div1{
                height: 250px;
                width: 250px;
                border: red 20px;
                background-color: cyan;
            }
            .div2{
                height: 150px;
                width: 150px;
                background-color: red;
                border-radius: 50%;

            }
            .ss li{
                color: gray;
                text-decoration: line-through;
            }
            .ssm li button{
                float: right;
            }
            .ssm li{
                width: 150px;
                height: 25px;
                
            }
        </style>
    </head>
    <body>
        <a href="http://www.bilibili.com">起飞</a>
        <p id="jihui">机会</p>
        <div class="div1">
            
        </div>
        <div class="div2"></div>
        n<big>m</big>s<big>l</big><br>
        <small>bzzb</small>
        <ol type="a" class="ssm">
            <li><span>起飞</span><button>完成</button></li>
            <li><span>肉蛋葱鸡<button>完成</button></span></li>
            <li><span>阿克曼</span><button>完成</button></li>
        </ol>
        <ol class="ss">
            <li>大一</li>
            <li>大二</li>
            <li>大三</li>
        </ol>
    </body>
</html>